i) Field of the Invention
The present invention relates to a controller of a generator mounted on a hybrid vehicle and a control method for this generator.
ii) Description of the Related Arts
As an electric vehicle, a so-called hybrid vehicle is well-known. In the vehicle of this kind, an engine is provided in addition to a motor as a driving source of the vehicle. For example, in a series hybrid vehicle, while an output of a battery such as a lead battery or the like mounted on the vehicle is supplied to the motor as driving power, an output of a generator driven by the engine is also supplied to this motor as the driving power. In this case, the generator and the battery connected in parallel are coupled with the motor and thus the battery can be charged using the output of the generator. That is, even when the battery is discharged during running of the vehicle, it is not necessary to charge this battery using an external power source. In other words, by driving the engine, the battery can be charged using the output of the generator. Moreover, the driving power of the motor can be supplied from not only the battery but also the generator, and the battery can be miniaturized.
In the case of using the battery such as the lead battery or the like mounted on the hybrid vehicle, by maintaining the state of charge (SOC) of the battery at approximately 70 to 80%, the life of the battery can be sugnificantly extended. Hence, it is preferable to control the SOC of the battery. As the controlling means for the SOC of the battery, for instance, a field current of a generator, that is, a generator output, is controlled to turn on or off, as disclosed in Japanese Patent Laid-Open No. Sho 57-202842.
However, in such a battery SOC control by controlling the generator output using the on/off control of the field current, it is difficult to accurately control the SOC of the battery in a predetermined range and to prevent overcharging. That is, simple on/off control of the field current often causes the SOC to go out of a target range and also causes overcharging of the battery in certain cases.
Further, when the motor is under heavy load, the generator output and the power of the battery are used for driving the motor. When this situation lasts for a long period of time, the battery is discharged and its SOC is significantly reduced. This SOC reduction brings about a short battery life.